Role of oceanic ozone deposition in explaining temporal variability in surface ozone at High Arctic sites

Abstract

Abstract. Dry deposition is an important removal mechanism for tropospheric ozone (O3). Currently, O3 deposition to oceans in atmospheric chemistry and transport models (ACTMs) is generally represented using constant surface uptake resistances. This occurs despite the role of solubility, waterside turbulence and O3 reacting with ocean water reactants such as iodide resulting in substantial spatiotemporal variability in O3 deposition and concentrations in marine boundary layers. We hypothesize that O3 deposition to the Arctic Ocean, having a relatively low reactivity, is overestimated in current models with consequences for the tropospheric concentrations, lifetime and long-range transport of O3. We investigate the impact of the representation of oceanic O3 deposition to the simulated magnitude and spatiotemporal variability in Arctic surface O3. We have integrated the Coupled Ocean-Atmosphere Response Experiment Gas transfer algorithm (COAREG) into the mesoscale meteorology and atmospheric chemistry model Polar-WRF-Chem (WRF) which introduces a dependence of O3 deposition on physical and biogeochemical drivers of oceanic O3 deposition. Also, we reduced the O3 deposition to sea ice and snow. Here, we evaluate WRF and CAMS reanalysis data against hourly averaged surface O3 observations at 25 sites (latitudes > 60∘ N). This is the first time such a coupled modeling system has been evaluated against hourly observations at pan-Arctic sites to study the sensitivity of the magnitude and temporal variability in Arctic surface O3 on the deposition scheme. We find that it is important to nudge WRF to the ECMWF ERA5 reanalysis data to ensure adequate meteorological conditions to evaluate surface O3. We show that the mechanistic representation of O3 deposition over oceans and reduced snow/ice deposition improves simulated Arctic O3 mixing ratios both in magnitude and temporal variability compared to the constant resistance approach. Using COAREG, O3 deposition velocities are in the order of 0.01 cm s−1 compared to ∼ 0.05 cm s−1 in the constant resistance approach. The simulated monthly mean spatial variability in the mechanistic approach (0.01 to 0.018 cm s−1) expresses the sensitivity to chemical enhancement with dissolved iodide, whereas the temporal variability (up to ±20 % around the mean) expresses mainly differences in waterside turbulent transport. The mean bias for six sites above 70∘ N reduced from −3.8 to 0.3 ppb with the revision to ocean and snow/ice deposition. Our study confirms that O3 deposition to high-latitude oceans and snow/ice is generally overestimated in ACTMs. We recommend that a mechanistic representation of oceanic O3 deposition is preferred in ACTMs to improve the modeled Arctic surface O3 concentrations in terms of magnitude and temporal variability.

Technical note: Quality assessment of ozone reanalysis products and gap-filling over subarctic Europe for vegetation risk mapping

“…Based on this generalized ozone climatology, we assessed the quality of available global (MACC and CAMSRA) and regional (CAM-SRAQ) reanalysis products for northern Fennoscandia focusing on the seasonality of ozone. We confirm previously published results concerning the quality of global reanalysis products (Huijnen et al, 2020;Barten et al, 2021) and find that the observed ozone patterns in northern Fennoscandia are not reproduced well. Better performance was displayed by the regional model reanalysis CAMSRAQ ensemble which reproduces the observed ozone seasonality well, although with a remaining annual average deviation of up to −7 ppb.…”

“…In terms of atmospheric chemistry, this includes meteorological data as well as observations of chemical substances from, for example, satellite, airborne instruments, and ground-level monitoring station networks. Global reanalyses, however, have already been shown to underestimate [O 3 ] particularly over the polar region (Huijnen et al, 2020;Barten et al, 2021). Barten et al (2021) suggest that global reanalysis products that only assimilate satellite products do not sufficiently cover [O 3 ] variations.…”

“…Global reanalyses, however, have already been shown to underestimate [O 3 ] particularly over the polar region (Huijnen et al, 2020;Barten et al, 2021). Barten et al (2021) suggest that global reanalysis products that only assimilate satellite products do not sufficiently cover [O 3 ] variations. The large discrepancies can be explained by the low spatiotemporal resolution not capturing atmospheric boundary layer dynamics and missing processes such as mechanistic oceanatmosphere O 3 exchange.…”

Arctic tropospheric ozone: assessment of current knowledge and model performance

“…However, other model deficiencies could also play a role, including dry deposition and NO x lifetime. Indeed, Barten et al (2021) found that overestimation of oceanic O 3 deposition can explain some differences between modeled and measured surface O 3 in the high Arctic. Some models in Fig.…”

Radiative impact of improved global parameterisations of oceanic dry deposition of ozone and lightning-generated NOx

“…Using the improved (or new) parameterisation, Luhar et al (2018) estimated an oceanic dry deposition of 98.4 ± 30.0 Tg O 3 yr −1 and a global one of 722.8 ± 87.3 Tg O 3 yr −1 (averaged over the years 2003-2012), which can be compared with the respective values 340 and 978 ± 127 Tg O 3 yr −1 obtained by Hardacre et al (2015) based on 15 global chemistry transport models (for the year 2001) using Wesely's scheme, demonstrating the large reduction in the oceanic value using the new parameterisation. The new approach was recently evaluated by other researchers in both global and regional models with various changes to the input parameter values (Loades et al, 2020;Barten et al, 2021).…”